The present invention relates to fluid controllers of the type which are utilized to control the flow of fluid from a fluid source to one or more fluid pressure operated devices, and more particularly, to such controllers of the type in which the controller valving is capable of providing two different types of valving action, one in response to rotary actuation, and the other in response to axial actuation.
Although the present invention may be utilized in various types of fluid controllers, having various types of valving, it is especially adapted for use in a fluid controller of the type including a rotatable valve spool and a relatively rotatable, follow-up valve sleeve. In the conventional, prior art controller, the valving action performed within the controller was in response to relative rotation between the spool and sleeve, typically initiated by rotation of a vehicle steering wheel, controlling the flow of fluid from a source to a vehicle power steering cylinder.
In related U.S. Pat. No. 5,016,672, assigned to the assignee of the present invention, the spool and sleeve define not only the conventional main fluid path in response to rotary valve actuation, but also, the spool and sleeve define a parallel fluid path in response to axial motion of the sleeve relative to the spool and housing. In the cited patent, the axial motion of the sleeve can be in either axial direction from a neutral axial position, and is achieved in response to some sort of pilot pressure, acting on one end of the sleeve, or the other.
In a fluid controller in which there is both rotary valve actuation and axial valve actuation, the conventional leaf-spring type of neutral centering arrangement may not be fully satisfactory. The centering spring arrangement must perform the basic function of biasing the spool and sleeve to their relative neutral rotary position, while at the same time, permitting relative axial motion therebetween. In addition, the centering spring arrangement must not provide a leakage path or "short-circuit" of any pressurized fluid being used as a pilot pressure.